1. Field of the Invention
The present invention relates to a thin film transistor, a method of manufacturing the same and a flat panel display device having the same, and more particularly to a thin film transistor which has an oxide semiconductor as an activation layer, a method of manufacturing the same and a flat panel display device having the same.
2. Description of the Related Art
A thin film transistor generally includes an activation layer which provides a channel region, a source region, and a drain region, and a gate electrode which is formed on the channel region and electrically insulated from the activation layer by a gate insulating film.
The activation layer of the thin film transistor formed as described above is generally formed of a semiconductor material, such as amorphous silicon or poly-silicon. However, if the activation layer of the thin film transistor is formed of amorphous silicon, it is difficult to implement a driving circuit operating at high speed due to low mobility. Meanwhile, if the activation layer is formed of poly-silicon, mobility is high, but a separate compensation circuit should be added due to uneven threshold voltage.
Also, a conventional method of manufacturing a thin film transistor using a low temperature poly-silicon (LTPS) involves an expensive process such as a laser annealing and has difficulty in property control, so it is difficult to be applied to a large-area substrate.
A study using an oxide semiconductor as an activation layer has been recently conducted in order to solve the problems.
Japanese Laid-Open Patent Publication No. 2004-273614 discloses a thin film transistor which has zinc oxide (ZnO) or an oxide semiconductor having zinc oxide (ZnO) as a main ingredient, as an activation layer.
The compound semiconductor having zinc oxide (ZnO) as a main ingredient is evaluated as a stable material, having an amorphous shape. If such a compound semiconductor is used as an activation layer, the compound semiconductor has various advantages in that the thin film transistor may be manufactured at a low temperature below 350° C. using the existing processing equipment, without additionally buying separate processing equipments, and an ion implantation process may be omitted.
However, there is a need for the development of process and the improvement of property capable of satisfying the electrical property in order to apply the oxide semiconductor to the device.